SEISMIC CHARACTERISTICS OF DEEPWATER CHANNEL SYSTEM IN NORTHWESTERN MARGIN OF SOUTH CHINA SEA AND ITS EVOLUTION

High-quality 2D seismic data are used in this paper to investigate the depositional pattern and morphologic features of the deepwater channel system and its evolutionary history. The deep water channel system starts from the Yinggehai Basin and through the Qiongdongnan Basin terminates in the Shuangfeng Basin. The system can be divided into four parts:central canyon-channel system, channel-lobe transitional zone, channel-lobe system, and the margin of the channel-lobe system. Study of the evolution of the four parts on shape, erosion depth, width, aggradations, and internal fillings has been carried out by the authors. The development of channel-levee and the width of the central channel system are controlled by the style of the slopes, of which there are five types. The channel-lobe transitional zone incises into the bottom sediments at the canyon mouth, and then rapidly expands due to weakening of topographical constraint. The unconfined channel-lobe system, located on the Shuangfeng Basin, is characterized by stretching levees for about thousands of meters and lateral aggradational deposits. The system losed its erosional ability finally, and terminated as a sand sheet.